Process of recovering ammonia from gases containing same



June 1927.

R. O. E. DAVIS ET AL PROCESS OF RECOVERING AMMONIA FROM GASES CONTAININGSAME Filed June 13, 1921 N Q Y gas leaving the cooling chamber isPatented June 7, 1927.

UNITED STA ROYALL O. E.

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PERU, NEBRASKA.

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Application am June is, 1921.- mm No. 47am.

(Qumran mmn an A6! or union ajma; 2: sum. 1.; eat.)

The invention described herein ma be used by the Government, or an oremployees in prosecution Government, or by1 out payment to us of anyUnited States, wit royalty thereon.

of itso cars 0 any other person in the K This invention relates to therecovery of ammonia from mlxtures containing the same in admixture withits gaseous elements and has for its principal objects the eflicient andeconomical separation of ammonia from such mixtures without thecontamination of the residual gaseous elements with catalyst oisons .orother substances which tend to redhce the'efliciency of"catalysts' ofthe' type such as are I synthesis of ammonia ments.

' In the removalin the catalytic nitro en fixationammonia is'oommon yremoved This hasthe disadvantage,

tion inwater. however that the "troduced to the catalyst chamber tendsto,

reduce the efliciency, especiall catalyst. If, ;on the other monia isremoved tial pressure the temperatures employed in the direct of ammoniafrom gases rocess the y absorp water vapor thereby -1nof-a sensitive byrefrigeration the parof the ammonia is'such that at employed toaccomplish such liquefaction about one percent of the ammonia.

As this gas returns to the' catalyst-cham 'ber. the efiiciency of thecatalyst 18 reduced.

thereby Our. investigations have led tothe discovery that certain salts,

particularly inorabove stated give a as become liquid arge quantities ofhave a low vapor temperatures around higher temperatures,

perature of operation,

-. readily evolved. 5

Among suitable for producing li absorbing ammonia are .';t

' liquefy with small amount ammonia at- 0 4 yapor pressure 0t and in soammoma-.. -'Ihes el1qu1ds pressure-of ammonia at the "salts which .wevhave found uids capable; of

low vapor pressure: 0

work for thefrom its gaseous eleand, the am- ;.to evolve, I n nd -(4)- asepatntion'tbithe ahdo'ing absorb zero" but- 'at' somewhat over therangeof tem- I the ammonia will be -m ent. ose, which will" ammonia orammonia and i a of-water and which will. as

' f that the absorbent' can be recirculated.

and a-relatively high, 7 ammonia but a negligible water vapor pressure"throughout the higher range ofo ierating temperatures be .65 mg salts.such asithium-nitrate (LiNO calcium nitrate (Ca)NO,) ammonium mtrate-(NH,NO,), ammonium thiocyanate- .(NH,CNS), sodium iodide (NaI), calciumapparatus, "lithium nitrate'or calcium nitrate ,may be employed butwhere the corrosive action of solutions upon iron is'not objectionablesuch salts as ammonium nitrate' or 9 tl'nocyanate or otherccorrosivesalts of those above. spec fied may be satisfactorily 'pleiy ed v 1g. 1is a view in elevation of an app in which view solidarrowshave been--ratus suitable for carrying out: the proce 76 to, indicate the flowlofliquid-while arrows are used .to indicate the flow of gas; "F1g 2, is avertical section through-one of thetowers.- 4.80

Our process canbecarried outfbyhny' means which causes (1) a stream ofgasconr taining ammonia to flowv through the liquid,

absorbent while-keeping-suid liquid iabso'rbif ent sufiicien'tly cool tosecure --efiectifaub sorption of the ammonia, (2) .a'se amtion c u Y theabsorbent containing absor j ammonia 651 from contact with the gases,'-.(3)"- 1- temperature of the7 absorbent elther partially. or? the 0sorbent and the ammtiniaevoly'e'dfw f m .In the preferred manner gf t m{a tion' of the ammonianis evolved as will alow the absorbent to remainin a liquid state-so.

through the scrubbing apparatus. In theaccompanying drawing,

forms a part hereof, we have illustrated one practical apparatus whichmay be employed in carrying out our process, it being understood thatthe specific apparatus herein shown forms no part of the presentinvention, nor do we intend thereby to limit ourselves to the use of anyspecific apparatus in carryingout said invention.

As shown by way of illustration the apparatus includes a series oftowers, preferably 3 in number, as designated by the reference numerals1, 2 and 3, and a separator a. In this apparatus the gas which is to bescrubbed is admitted through the gas inlet pipe 6, passing thencethrough an ordinary T-joint 1' down through the long tube 7 to tower 1,and up through the absorbent liquid and out of said tower through pipe.8, and T-joint 2, to the tube 9 in tower 2, and thence up through theliquid in-tower 2, and out of the tower through pipe 10,

through coil 11, pipe 12, T-joint 3' down through the tube 13 in tower3, from whence it rises through the liquid and passes out of tower 3through the gas exit pipe 14.

The absorbent liquid is forced through the towers by means of acirculating pump,

not shown, from which pump it passes down through pipe 15, coil 16, topipe 17 ,T-joint 3', and .down through tube 13 in tower 3 and out ofpipe 18 connected at the bottom of tower 3, through T-joint 2',down'through tube 9, in tower 2, and out through pipe l9 to T-joint 1,down through pipe 7, in tower 1, and out through pipe 21 to thes'eparator 4, and from thence through pipe'22 to the circulating pump,from which" pump it is again forced through the apparatus as here toforedescribedf From the foregoing it will be seen that the gases first-freedof their ammonia leave the last tower 3,'which is cooled to about 0 C.by the cooling coil 5 to maintain a low "ammonia vapor pressure, and areconducted back to the catalyst or used for such other operations as mayrequire gas with less than 1% of ammonia. The liquid absorbent Y whichflows from tower -1 to the separator d is heated in an suitable manneras illustrated by the coil 23 which is of suflicient capacity to heatthe liquid while flowing through'the separator to about 40 to 50 C. anddrive off a ortion of the ammonia bviously, the ammonia liberated may becollected either as liquid ammonia, absorbed inwater or acid or utilized'in any other desired manner. The temperature maintained within tower 1may be determined by means of a 'pyrometer, a pyrometer' well 20 beingprovided forthat pur-L pose.

By way of illustration the following are given as examples of theabsorbent used, and

the solutions formed thereby when the absorbent is saturated withammonia at 0 C,

aesmeo With lithium nitrate (LiNO,) as an absorbent salt a solution of63.66% lLiNO and 36.34:% NH, is obtained or a solution of 35.51% LiNO38.43% NH and 6.06% n, 1

When. using calcium nitrate as the absorbent a solution of, 55.8% Ca(NO25.77% NH, and 18.43% H O is obtained.

The vapors" of such solutions at 0 C. show an indicated water vaporpressure of less than 1 mm.

Obviously the process may be carried out at ordinary pressure or atincreased pressures, such for example as pressures in excess of 100atmospheres, such as is commonly maintained in the process for thesynthesis of ammonia, or if preferred, the

absorption maybe conducted at high pres-.

sures and the removal at lower pressures.

Various modifications within the scope of the appended claims may bemade in the herein described process without departing from the spiritof our invention as covered by said claims.

Having thus described our invention, what we claim is:

1. The method of removing ammonia from gases which consists in absorbingthe ammonia from a gaseous mixture containing free ammonia in a fluidabsorbent substance therefor having a low vapor pressure of ammonia atapproximately zero degrees centigrade and a high vapor pressure ofammonia at temperatures between forty and fifty degrees centigrade,while maintaining said substance during said absorp'tion s'uflicientlycool to secure effective absorption of said ammonia and its separationfrom said gases under treatment, separating said absorbent containingsaid ammonia from contact with said gases and then raising thetemperature of the absorbent so separated -to a suflicient degree todrive oif absorbed recovering the abtherefor, including a salt having alow vapor pressure of ammonia at approximate- 1y zero degrees centigradeand a high vapor pressure of ammonia at temperatures between forty. andfifty degrees centigrade, while maintaining said liquid including suchsalt during said absorption sufficiently cool to secure effectiveabsorption of said ammonia andits separation fromsaid gases undertreatment, separating; said absorbent- .containing said ammonia fromcontact with said gases and then-raising the temperature of theabsorbent so separated to a sufficient degree to drive off absorbedammonia and separately recovering the absorbent and the ammonia. V

ion

therefor, including 3. The method of removing ammonia from gases whichconsists in absorbing the ammonia from a gaseous mixture containingfreeammonia ,in a liquid absorbent an inorganic salt, having a low vaporpressure of ammonia at approximately zero degrees Centigrade and a highpressure of ammonia at temperatures between forty and fifty degreescentigrade, While maintaining said liquid including such inorganic saltduring said absorption sufiicently cool to secure effective absorptionof said ammonia and its separation from said gases under treatment,separating'said absorbent containing said ammonia from contact with saidgases. and then raising the temperature of the absorbent so separated toa suflicient degree to drive ofi absorbed ammonia and separatelyrecovering the absorbent and the ammonia.

4. The method of removing ammonia from gases which consists in absorbingthe ammonia from a gaseous mixture containing free ammonia in a fluidabsorbent substance, which is substantially non-corrosive to ordinarysteel and iron apparatus and has a low vapor pressure of ammonia atapproximately zero degrees centigrade and a high vapor pressure ofammonia at temperatures between forty and fifty degreescentigrade, ingsaid absorption sufliciently cool to secure effective absorption of saidammonia and its separation fromsaid gases undertreat- -ment, separatingsaid absorbent containing said ammonia from contact with said gases andthen raising the temperature of the absorbent so separated to asuflicient degree to drive of? absorbed ammonia and separate- 1yrecovering the absorbent and ammonia.

5. The method of removing ammonia from gases which consists in absorbinthe ammonia from a gaseous mixture containing while maintaining saidsubstance dur-' ment, separating said absorbent containing said ammoniafrom contact with said gases and then raising the temperature of theabsorbent so separated to a sufiicient degree to drive 01f absorbedammonia and separately recovering the absorbent and ammonia.

6. The method of removing ammonia from gases which consists in absorbingthe ammonia from a gaseous mixture containing free ammonia in aninorganic nitrate, while maintaining said nitrate during said absorptionsufiiciently cool to secure effective absorption of said ammonia and itsseparation from said gases under treatment, separating said absorbentcontaining said ammonia from contact with said gases and then raisingthe temperature of the absorbent so separated to a suflicient degree todrive off absorbed ammonia and separately recovering the absorbent andammonia,

7. The method of removing ammonia from gases which consists in absorbingthe ammonia from ,a gaseous mixture containing free ammonia in lithiumnitrate, while maintaining said lithium nitrate during said absorptionsufliciently cool to secure effective absorption of said ammonia and itsseparation from said gases under treatment, separating said absorbentcontaining said ammonia from contact with said gases and then raisingthe temperature of the absorbent so separated to a sufiicient degree toevolve a part of the ammonia and separately recovering the absorbent andammonia so evolved therefrom.

ROYALL O. E. DAVIS. LEWIS B. OLMSTEAD.

